1. Field of the Invention
This invention relates to a solid catalyst component for .alpha.-olefin polymerization and a process for producing the same. More particularly it relates to the above-mentioned solid catalyst component capable of yielding .alpha.-olefin polymer powder having a good dispersibility of powdery additives therein, and a process for producing the same.
2. Description of the Prior Art
.alpha.-Olefin polymers have been used for various and wide application uses. Among the polymers, crystalline polypropylene has been broadly used also in the fields of film and sheet due to its superior mechanical properties and optical properties and further advantages of non-toxicity, odorless properties and others. If polypropylene film and sheet (hereinafter referred to as polypropylene film, etc.) have inferior slip properties and blocking resistance, or if they have an insufficient stiffness or transparency, then powdery additives are often added to polypropylene in advance to improve these physical properties. Such addition makes it possible to impart fine projections and depressions on the surface of polypropylene film, etc.
The average particle diameter of such powdery additives is generally 20 microns or smaller and 0.005 micron or larger, and the smaller the particle diameter, often the better the results obtained, for practical use. Whether the dispersibility of such powdery additives in .alpha.-olefin polymers (hereinafter abbreviated to polymers) is good or not is ruled by the shape and particle size distribution of the polymer powder.
Namely, the nearer to sphere the shape of the polymer powder and also the narrower the width of the particle size distribution, the inferior the dispersibility. If the dispersion of the powdery additives in a composition consisting of the polymer powder and the powdery additives is inferior such that the dispersion is heterogeneous or agglomeration of the additives is partly observed, then the following problems are raised with the film or sheet obtained by molding the composition: .circle.1 disorder of projections and depressions of the film, etc. (non-uniformity); .circle.2 inferior appearance and transparency due to uneven dispersion of the additives; .circle.3 occurrence of fish eyes; .circle.4 insufficient stiffness due to no addition effectiveness of the additives; and others.
The above problems may be regarded as technical problems which have occurred accompanying the fact that the shape and particle size distribution of the polymer powder has been, so to speak, improved.
As one of the processes for producing the polymer powder of such shape (note: .alpha.-olefin polymerization processes), the present inventors have previously provided processes for producing .alpha.-olefin polymer particles having a shape near to sphere, a small average particle diameter and a narrow particle size distribution (Japanese patent application laid-open Nos. Sho 56-119,707/1981 and Sho 56-120,712/1981). The catalysts used in these polymerization processes have a notably improved storage-stability and heat stability, and also a high catalyst activity, and further the resulting polymers have a high bulk density and crystallinity. Still further, since the polymer particles have a spherical shape, there has been an advantage that production and subsequent handling of the polymer are easy.
However, as already described above, the shape of the polymer powder produced using such catalysts has brought about a new problem of inferior dispersibility of the powdery additives as mentioned above.
Namely, according to the above-mentioned inventions of the present inventors, the average particle diameter of the resulting polymer powder is as large as 200 to 500 microns, its shape is spherical and the content of fine particles therein is low; thus there has been a problem in the point of the uniformity of dispersion of the additives in the composition obtained by blending the powdery additives to the above-mentioned polymers.
As one of the processes for improving the dispersibility of the powdery additives in the polymer powder, there is a process of making coexistent with the matrix polymer powder, a considerably large quantity of fine particle polymer. In order to improve the dispersibility, however, it is necessary to make a polymer having a particle diameter of 50 microns or less coexistent in 20% by weight or more. However, as to such a superfine polymer, there is a fear that it may cause handling troubles such that in the polymer production process, it may scatter away during its transportation or its drying step or clog the transportation pipe.
On the other hand, the solid catalyst component per se for producing such a superfine polymer is required to far reduce its particle diameter, but such a solid catalyst component is difficult to produce. Namely, such a solid catalyst component having a superfine particle diameter may be considerably lost at the time of washing and drying in its production process, resulting in reduction of yield or reduction of the capacity of the production apparatus. Further, as to the solid catalyst component having a superfine particle diameter, an abnormal reaction may occur at the time of its use i.e. at the time of .alpha.-olefin polymerization such that the proportion of atactic polypropylene formed as a by-product at the time of production of polypropylene may increase notably.
The present inventors have made extensive research in order to find a solid catalyst component for .alpha.-olefin polymerization, capable of solving the above various problems, and as a result have found that when TiCl.sub.4 is reduced with a reducing agent comprising a specified organoaluminum compound derivative to produce a solid intermediate, if there is employed an agitation intensity for the reaction mixture in the reactor, defined by definite values of agitation power and baffle ratio as defined later, followed by carrying out necessary production process, then a solid catalyst component for .alpha.-olefin polymerization, having an average particle diameter of 2 to 10 microns and a spherical shape is obtained, which can solve the above various problems, and have accomplished the present invention.
As is apparent from the foregoing, the object of the present invention (in two aspects) is to provide a solid catalyst component for .alpha.-olefin polymerization which, when produced, does not cause the above-mentioned troubles, and when used, yields a polymer having a suitably less particle size and a high bulk density without increasing the quantity of atactic polymer byproduced, which polymer affords a very good dispersibility of powdery additives therein in spite of its narrow particle size distribution and spherical shape; and a process for producing the same. Other objects of the present invention will be apparent from the succeeding description.